Will this strike the U.S. at the same time as Canada, and elsewhere as well, to create a maximum shock, or will it be done region by region with the rest of the world able to observe the crushing results and the helplessness of those in its path?

You have seen intuitively, that there are variations in possibilities here. While a worldwide shutdown would be the most dramatic demonstration of extraterrestrial power, it would create even greater drama to see it happen region by region, so people would have a kind of advanced warning that if it's happening in one region, then in another, it might keep going and reach them personally as well. The time for this to play out creates a growing tidal wave of fear and will heighten the societal turmoil and acts of desperation, adding pain and suffering as people rush to acquire provisions and backup support, sources of power, and so on, to help save themselves when their turn comes. That will add significantly further economic and emotional trauma to the picture because it will be a dramatic fear factory, a rolling thunder of destruction, and the message will be clear that something is exerting great power that humans are unable to stop.